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  • 1.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Solar Wind Dynamics within The Atmosphere of comet 67P/Churyumov-Gerasimenko2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, we explore the dynamics of the solar wind as it perme-ates and flows through a tenuous cometary atmosphere, with a focuson the interaction observed at comet 67P/Churyumov–Gerasimenko.

    Seven comets had already been visited by nine different probes when the European spacecraft Rosetta reached comet Churyumov–Gerasimenko in August 2014. The mission was however the first to orbit its host comet, which it did for a total duration of more than two years, corre-sponding to a large part of the comet’s orbit around the Sun. This en-abled to study how the dynamics of the plasma environment evolvedas the comet itself was transformed from one of the smallest obstaclesto the solar wind in the Solar System when far away from the Sun, toa well-established magnetosphere at perihelion.

    Most of our efforts tackle the early part of this transformation, when the creation of new-born cometary ions starts to induce significant disturbances to the incident flow. During this stage, a kinetic descrip-tion of the interaction is necessary, as the system of interest cannot be reduced to a hydrodynamic problem. This contrasts with the situation closer to the Sun, where a fluid treatment can be used, at Churyumov–Gerasimenko as well as at previously visited comets.

    Rosetta was not a mission dedicated to plasma studies, however. It directly translates into a limited spatial coverage of the cometary plasma environment, which by its nature extends over several spatial scales. An approach solely based on the analysis of in-situ data cannot properly address the major questions on the nature and physics of the plasma environment of Churyumov–Gerasimenko. This thesis there-fore largely exploits the experimental–analytical–numerical triad of approaches. In Chapters 3 and 4 we propose simple models of the ion dynamics and of the cometary plasma environment, and these are tested against experimental and numerical data. Used together,they give a global description of the solar wind ion dynamics through the cometary atmosphere, that we explore in the 2-dimensional and 3-dimensional cases (Chapter 5). In Chapter 6, we propose a view onthe interaction and its fluid aspects when closer to the Sun.

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  • 2.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Lindkvist, Jesper
    Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Holmström, Mats
    Swedish Institute of Space Physics, Kiruna.
    Stenberg-Wieser, G.
    Swedish Institute of Space Physics, Kiruna.
    Ramstad, Robin
    Swedish Institute of Space Physics, Kiruna.
    Götz, C.
    Technicsche Universität Braunschweig, Institute for Geophysics and Extraterrestrial Physics, Braunschweig.
    Mass-loading of the solar wind at 67P/Churyumov-Gerasimenko: Observations and modelling2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 596, article id A42Article in journal (Refereed)
    Abstract [en]

    Context. The first long-term in-situ observation of the plasma environment in the vicinity of a comet, as provided by the European Rosetta spacecraft. Aims. Here we offer characterisation of the solar wind flow near 67P/Churyumov-Gerasimenko (67P) and its long term evolution during low nucleus activity. We also aim to quantify and interpret the deflection and deceleration of the flow expected from ionization of neutral cometary particles within the undisturbed solar wind. Methods. We have analysed in situ ion and magnetic field data and combined this with hybrid modeling of the interaction between the solar wind and the comet atmosphere. Results. The solar wind deflection is increasing with decreasing heliocentric distances, and exhibits very little deceleration. This is seen both in observations and in modeled solar wind protons. According to our model, energy and momentum are transferred from the solar wind to the coma in a single region, centered on the nucleus, with a size in the order of 1000 km. This interaction affects, over larger scales, the downstream modeled solar wind flow. The energy gained by the cometary ions is a small fraction of the energy available in the solar wind. Conclusions. The deflection of the solar wind is the strongest and clearest signature of the mass-loading for a small, low-activity comet, whereas there is little deceleration of the solar wind

  • 3.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Alho, M.
    Aalto University, School of Electrical Engineering, Department of Electronics and Nanoengineering, Finland.
    Goetz, C.
    Technische Universität Braunschweig, Institute for Geophysics and Extraterrestrial Physics, Germany.
    Tsurutani, B.
    Jet Propulsion Laboratory, California Institute of Technology, USA.
    The birth and growth of a solar wind cavity around a comet: Rosetta observations2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, no Suppl. 2, p. S369-S403Article in journal (Refereed)
    Abstract [en]

    The Rosetta mission provided detailed observations of the growth of a cavity in the solar wind around comet 67P/Churyumov–Gerasimenko. As the comet approached the Sun, the plasma of cometary origin grew enough in density and size to present an obstacle to the solar wind. Our results demonstrate how the initial slight perturbations of the solar wind prefigure the formation of a solar wind cavity, with a particular interest placed on the discontinuity (solar wind cavity boundary) passing over the spacecraft. The slowing down and heating of the solar wind can be followed and understood in terms of single particle motion. We propose a simple geometric illustration that accounts for the observations, and shows how a cometary magnetosphere is seeded from the gradual steepening of an initially slight solar wind perturbation. A perspective is given concerning the difference between the diamagnetic cavity and the solar wind cavity.

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  • 4.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Henri, P.
    LPC2E, CNRS, Orléans.
    Berecic, L.
    Swedish Institute of Space Physics, Kiruna.
    Nicolaou, G.
    Swedish Institute of Space Physics, Kiruna.
    Stenberg-Wieser, G.
    Swedish Institute of Space Physics, Kiruna.
    Wieser, M.
    Swedish Institute of Space Physics, Kiruna.
    Tabone, B.
    LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris.
    Saillenfest, M.
    IMCCE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris.
    Goetz, C.
    Technische Universität Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
    The root of a comet tail: Rosetta ion observations at comet 67P/Churyumov–Gerasimenko2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, article id A21Article in journal (Refereed)
    Abstract [en]

    Context.The first 1000 km of the ion tail of comet 67P/Churyumov–Gerasimenko were explored by the EuropeanRosettaspacecraft,2.7 au away from the Sun.Aims.We characterised the dynamics of both the solar wind and the cometary ions on the night-side of the comet’s atmosphere.Methods.We analysed in situ ion and magnetic field measurements and compared the data to a semi-analytical model.Results.The cometary ions are observed flowing close to radially away from the nucleus during the entire excursion. The solar windis deflected by its interaction with the new-born cometary ions. Two concentric regions appear, an inner region dominated by theexpanding cometary ions and an outer region dominated by the solar wind particles.Conclusions.The single night-side excursion operated byRosettarevealed that the near radial flow of the cometary ions can beexplained by the combined action of three different electric field components, resulting from the ion motion, the electron pressuregradients, and the magnetic field draping. The observed solar wind deflection is governed mostly by the motional electric field−uion×B.

  • 5.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Wieser, Gabriella Stenberg
    Swedish Institute of Space Physics.
    Nemeth, Zoltan
    Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest.
    Brolles, T.W.
    Space Science and Engineering Division, Southwest Research Institute, San Antonio.
    Richter, Ingo
    Technische Universität–Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
    Mass loading at 67P/Churyumov-Gerasimenko: A case study2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 4, p. 1411-1418Article in journal (Refereed)
    Abstract [en]

    We study the dynamics of the interaction between the solar wind ions and a partially ionized atmosphere around a comet, at a distance of 2.88 AU from the Sun during a period of low nucleus activity. Comparing particle data and magnetic field data for a case study, we highlight the prime role of the solar wind electric field in the cometary ion dynamics. Cometary ion and solar wind proton flow directions evolve in a correlated manner, as expected from the theory of mass loading. We find that the main component of the accelerated cometary ion flow direction is along the antisunward direction and not along the convective electric field direction. This is interpreted as the effect of an antisunward polarization electric field adding up to the solar wind convective electric field.

  • 6.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Tabone, B.
    LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Dawn-dusk asymmetry induced by the Parker spiral angle in the plasma dynamics around comet 67P/Churyumov-Gerasimenko2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 478, no 2, p. 1570-1575Article in journal (Refereed)
    Abstract [en]

    When interacting, the solar wind and the ionised atmosphere of a comet exchange energy and momentum. Our aim is to understand the influence of the average Parker spiral configuration of the solar wind magnetic field on this interaction. We compare the theoretical expectations of an analytical generalised gyromotion with Rosetta observations at comet 67P/Churyumov-Gerasimenko. A statistical approach allows one to overcome the lack of upstream solar wind measurement. We find that additionally to their acceleration along (for cometary pick-up ions) or against (for solar wind ions) the upstream electric field orientation and sense, the cometary pick-up ions are drifting towards the dawn side of the coma, while the solar wind ions are drifting towards the dusk side of the coma, independent of the heliocentric distance. The dynamics of the interaction is not taking place in a plane, as often assumed in previous works.

  • 7.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Tabone, B.
    LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris.
    Saillenfest, M.
    IMCCE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris.
    Henri, P.
    LPC2E, CNRS, Orléans.
    Deca, J.
    Laboratory for Atmospheric and Space Physics (LASP), University of Colorado Boulder.
    Lindkvist, J.
    Umeå University, Department of Physics.
    Holmström, Mats
    Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Solar wind dynamics around a comet: A 2D semi-analytical kinetic model2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 620, article id A35Article in journal (Refereed)
    Abstract [en]

    Aims.We aim at analytically modelling the solar wind proton trajectories during their interaction with a partially ionised cometaryatmosphere, not in terms of bulk properties of the flow but in terms of single particle dynamics.Methods.We first derive a generalised gyromotion, in which the electric field is reduced to its motional component. Steady-stateis assumed, and simplified models of the cometary density and of the electron fluid are used to express the force experienced byindividual solar wind protons during the interaction.Results.A three-dimensional (3D) analytical expression of the gyration of two interacting plasma beams is obtained. Applying it to acomet case, the force on protons is always perpendicular to their velocity and has an amplitude proportional to 1/r2. The solar winddeflection is obtained at any point in space. The resulting picture presents a caustic of intersecting trajectories, and a circular regionis found that is completely free of particles. The particles do not lose any kinetic energy and this absence of deceleration, togetherwith the solar wind deflection pattern and the presence of a solar wind ion cavity, is in good agreement with the general results of theRosettamission.Conclusions.The qualitative match between the model and thein situdata highlights how dominant the motional electric field isthroughout most of the interaction region for the solar wind proton dynamics. The model provides a simple general kinetic descriptionof how momentum is transferred between these two collisionless plasmas. It also shows the potential of this semi-analytical modelfor a systematic quantitative comparison to the data.

  • 8.
    Berecic, Laura
    et al.
    Swedish Institute of Space Physics, Kiruna.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Nicolaou, G.
    Swedish Institute of Space Physics, Kiruna.
    Stenberg-Wieser, G.
    Swedish Institute of Space Physics, Kiruna.
    Wieser, M.
    Swedish Institute of Space Physics, Kiruna.
    Goetz, C.
    Technische Universität Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
    Cometary ion dynamics observed in the close vicinity of comet 67P/Churyumov-Gerasimenko during the intermediate activity period2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 613, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Aims.Cometary ions are constantly produced in the coma, and once produced they are accelerated and eventually escape the coma.We describe and interpret the dynamics of the cometary ion flow, of an intermediate active comet, very close to the nucleus and in theterminator plane.Methods.We analysed in situ ion and magnetic field measurements, and characterise the velocity distribution functions (mostly usingplasma moments). We propose a statistical approach over a period of one month.Results.On average, two populations were observed, separated in phase space. The motion of the first is governed by its interactionwith the solar wind farther upstream, while the second one is accelerated in the inner coma and displays characteristics compatiblewith an ambipolar electric field. Both populations display a consistent anti-sunward velocity component.Conclusions.Cometary ions born in different regions of the coma are seen close to the nucleus of comet 67P/Churyumov–Gerasimenko with distinct motions governed in one case by the solar wind electric field and in the other case by the position relative tothe nucleus. A consistent anti-sunward component is observed for all cometary ions. An asymmetry is found in the average cometaryion density in a solar wind electric field reference frame, with higher density in the negative (south) electric field hemisphere. Thereis no corresponding signature in the average magnetic field strengt

  • 9.
    Brolies, Thomas W.
    et al.
    Space Science and Engineering Division, Southwest Research Institute (SwRI).
    Burch, James L.
    Southwest Research Institute, 6220 Culebra Road, San Antonio, Space Science and Engineering Division, Southwest Research Institute (SwRI).
    Clark, Grace A.
    Heliophysics Division, Goddard Space Flight Center.
    Koenders, Christoph
    Institut für Geophysik und Extraterrestrische Physik, Technische Universität Braunschweig.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Goldstein, Raymond M.
    Space Science and Engineering Division, Southwest Research Institute (SwRI).
    Fuselier, Stephen Anthony
    Space Science and Engineering Division, Southwest Research Institute (SwRI).
    Mandt, Kathleen E.
    Space Science and Engineering Division, Southwest Research Institute (SwRI).
    Mokashi, Prachet
    Southwest Research Institute, 6220 Culebra Road, San Antonio, Space Science and Engineering Division, Southwest Research Institute (SwRI).
    Samara, M.
    Heliophysics Division, Goddard Space Flight Center.
    Rosetta observations of solar wind interaction with the comet 67P/Churyumov-Gerasimenko2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 583, article id A21Article in journal (Refereed)
    Abstract [en]

    Context. The Rosetta spacecraft arrived at the comet 67P/Churyumov-Gerasimenko on August 6, 2014, which has made it possible to perform the first study of the solar wind interacting with the coma of a weakly outgassing comet. Aims. It is shown that the solar wind experiences large deflections (>45°) in the weak coma. The average ion velocity slows from the mass loading of newborn cometary ions, which also slows the interplanetary magnetic field (IMF) relative to the solar wind ions and subsequently creates a Lorentz force in the frame of the solar wind. The Lorentz force in the solar wind frame accelerates ions in the opposite direction of cometary pickup ion flow, and is necessary to conserve momentum. Methods. Data from the Ion and Electron Sensor are studied over several intervals of interest when significant solar wind deflection was observed. The deflections for protons and for He++ were compared with the flow of cometary pickup ions using the instrument's frame of reference. We then fit the data with a three-dimensional Maxwellian, and rotated the flow vectors into the Comet Sun Equatorial coordinate system, and compared the flow to the spacecraft's position and to the local IMF conditions. Results. Our observations show that the solar wind may be deflected in excess of 45° from the anti-sunward direction. Furthermore, the deflections change direction on a variable timescale. Solar wind protons are consistently more deflected than the He++. The deflections are not ordered by the spacecraft's position relative to the comet, but large changes in deflection are related to changes in the orthogonal IMF components

  • 10.
    Ekman, Jonas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Martin-Torres, Javier
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Emami, Reza
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Törlind, Peter
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Öhrwall Rönnbäck, Anna
    Gustafsson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zorzano Mier, María-Paz
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Milz, Mathias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Parida, Vinit
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Wolf, Veronika
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Dordlofva, Christo
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Mendaza de Cal, Maria Teresa
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Jamali, Maryam
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Roos, Tobias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Ottemark, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nieto, Chris
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Soria Salinas, Álvaro Tomás
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Vázquez Martín, Sandra
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nyberg, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Neikter, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindwall, Angelica
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Fakhardji, Wissam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Projekt: Rymdforskarskolan2015Other (Other (popular science, discussion, etc.))
    Abstract [en]

    The Graduate School of Space Technology

  • 11.
    Nicolaou, G.
    et al.
    Swedish Institute of Space Physics, SE-981 28 Kiruna, Sweden.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, SE-981 28 Kiruna, Sweden.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, SE-981 28 Kiruna, Sweden.
    Wieser, M.
    Swedish Institute of Space Physics, SE-981 28 Kiruna, Sweden.
    Yamauchi, M.
    Swedish Institute of Space Physics, SE-981 28 Kiruna, Sweden.
    Berčič, Laura
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, SE-981 28 Kiruna, Sweden.
    Stenberg Wieser, G.
    Swedish Institute of Space Physics, SE-981 28 Kiruna, Sweden.
    Energy-angle dispersion of accelerated heavy ions at 67P/Churyumov-Gerasimenko: Implication in the mass-loading mechanism2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, p. S339-S345Article in journal (Refereed)
    Abstract [en]

    The Rosetta spacecraft studied the comet 67P/Churyumov-Gerasimenko for nearly two years. The Ion Composition Analyzer instrument on board Rosetta observed the positive ion distributions in the environment of the comet during the mission. A portion of the comet's neutral coma is expected to get ionized, depending on the comet's activity and position relative to the Sun, and the newly created ions are picked up and accelerated by the solar wind electric field, while the solar wind flow is deflected in the opposite direction. This interaction, known as the mass-loading mechanism, was previously studied by comparing the bulk flow direction of both the solar wind protons and the accelerated cometary ions with respect to the direction of the magnetic and the convective solar wind electric field. In this study, we show that energy-angle dispersion is occasionally observed. We report two types of dispersion: one where the observed motion is consistent with ions gyrating in the local magnetic field and another where the energy-angle dispersion is opposite to that expected from gyration in the local magnetic field. Given that the cometary ion gyro-radius in the undisturbed solar wind magnetic and electric field is expected to be too large to be detected in this way, our observations indicate that the local electric field might be significantly smaller than that of the undisturbed solar wind. We also discuss how the energy-angle dispersion, which is not consistent with gyration, may occur due to spatially inhomogeneous densities and electric fields.

  • 12.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Burch, James L.
    Southwest Research Institute, San Antonio, TX, USA.
    Carr, Christopher M.
    Department of Physics, Imperial College London, London, UK.
    Eriksson, Anders I.
    Swedish Institute of Space Physics, Ångström Laboratory, Uppsala, Sweden.
    Glassmeier, Karl‐Heinz
    Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Braunschweig, Germany.
    Henri, Pierre
    Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, UMR 7328 CNRS – Université d'Orléans, Orléans, France.
    Galand, Marina
    Department of Physics, Imperial College London, London, UK.
    Goetz, Charlotte
    Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Braunschweig, Germany.
    Gunell, Herbert
    Royal Belgian Institute for Space Aeronomy, Brussels, Belgium; Department of Physics, Umeå University, Umeå, Sweden.
    Karlsson, Tomas
    Department of Space and Plasma Physics, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden.
    Birth of a Magnetosphere2021In: Magnetospheres in the Solar System / [ed] Romain Maggiolo; Nicolas André; Hiroshi Hasegawa; Daniel T. Welling, John Wiley & Sons, 2021, p. 427-440Chapter in book (Refereed)
    Abstract [en]

    A magnetosphere may form around an object in a stellar wind either due to the intrinsic magnetic field of the object or stellar wind interaction with the ionosphere of the object. Comets represent the most variable magnetospheres in our solar system, and through the Rosetta mission we have had the chance to study the birth and evolution of a comet magnetosphere as the comet nucleus approached the Sun. We review the birth of the comet magnetosphere as observed at comet 67P Churyumov–Gerasimenko, the formation of plasma boundaries and how the solar wind–atmosphere interaction changes character as the cometary gas cloud and magnetosphere grow in size. Mass loading of the solar wind leads to an asymmetric deflection of the solar wind for low outgassing rates. With increasing activity a solar wind ion cavity forms. Intermittent shock‐like features were also observed. For intermediate outgassing rate a diamagnetic cavity is formed inside the solar wind ion cavity, thus well separated from the solar wind. The cometary plasma was typically very structured and variable. The region of the coma dense enough to have significant collisions forms a special region with different ion chemistry and plasma dynamics as compared to the outer collision‐free region.  

  • 13.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics .
    Gunell, H.
    Belgian Institute for Space Aeronomy.
    Karlsson, T.
    Department of Space and Plasma Physics, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm.
    Brenning, N.
    Department of Space and Plasma Physics, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm.
    Henri, P.
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), UMR 7328 CNRS – Université d’Orléans.
    Goetz, C.
    Technische Universität Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
    Eriksson, A.I.
    Swedish Institute of Space Physics, Ångström Laboratory.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics.
    Stenberg-Wieser, G.
    Swedish Institute of Space Physics .
    Vallières, X.
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), UMR 7328 CNRS – Université d’Orléans.
    Size of a plasma cloud matters The polarisation electric field of a small-scale comet ionosphere2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, article id A50Article in journal (Refereed)
    Abstract [en]

    Context. The cometary ionosphere is immersed in fast flowing solar wind. A polarisation electric field may arise for comets much smaller than the gyroradius of pickup ions because ions and electrons respond differently to the solar wind electric field. Aims. A situation similar to that found at a low activity comet has been modelled for barium releases in the Earth's ionosphere. We aim to use such a model and apply it to the case of comet 67P Churyumov-Gerasimenko, the target of the Rosetta mission. We aim to explain the significant tailward acceleration of cometary ions through the modelled electric field. Methods. We obtained analytical solutions for the polarisation electric field of the comet ionosphere using a simplified geometry. This geometry is applicable to the comet in the inner part of the coma as the plasma density integrated along the magnetic field line remains rather constant. We studied the range of parameters for which a significant tailward electric field is obtained and compare this with the parameter range observed. Results. Observations of the local plasma density and magnetic field strength show that the parameter range of the observations agree very well with a significant polarisation electric field shielding the inner part of the coma from the solar wind electric field. Conclusions. The same process gives rise to a tailward directed electric field with a strength of the order of 10% of the solar wind electric field. Using a simple cloud model we have shown that the polarisation electric field, which arises because of the small size of the comet ionosphere as compared to the pick up ion gyroradius, can explain the observed significant tailward acceleration of cometary ions and is consistent with the observed lack of influence of the solar wind electric field in the inner coma.

  • 14.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Box 812, SE-981 28 Kiruna, Sweden.
    Stenberg Wieser, Gabriella
    Swedish Institute of Space Physics, Box 812, SE-981 28 Kiruna, Sweden.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Box 812, SE-981 28 Kiruna, Sweden.
    Gunell, Herbert
    Royal Belgian Institute for Space Aeronomy, Avenue Circulaire 3, B-1180 Brussels, Belgium; Department of Physics, Umeå University, SE-901 87 Umeå, Sweden.
    Wieser, Martin
    Swedish Institute of Space Physics, Box 812, SE-981 28 Kiruna, Sweden.
    Galand, Marina
    Department of Physics, Imperial College London, Prince Consort Road, London SW7 2AZ, UK.
    Simon Wedlund, Cyril
    Department of Physics, University of Oslo, PO Box 1048 Blindern, N-0316 Oslo, Norway.
    Alho, Markku
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, PO Box 15500, FI-00076 Aalto, Finland.
    Goetz, Charlotte
    Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Mendelssohnstr 3, D-38106 Braunschweig, Germany.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Box 812, SE-981 28 Kiruna, Sweden.
    Henri, Pierre
    LPC2E-CNRS, 3A avenue de la Recherche Scientifique, F-45071 Orléans, Cedex, 2, Orléans, France.
    Odelstad, Elias
    Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden.
    Vigren, Erik
    Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden.
    Evolution of the ion environment of comet 67P during the Rosetta mission as seen by RPC-ICA2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, no Suppl_2, p. S252-S261Article in journal (Refereed)
    Abstract [en]

    Rosetta has followed comet 67P from low activity at more than 3.6 au heliocentric distance to high activity at perihelion (1.24 au) and then out again. We provide a general overview of the evolution of the dynamic ion environment using data from the RPC-ICA ion spectrometer. We discuss where Rosetta was located within the evolving comet magnetosphere. For the initial observations, the solar wind permeated all of the coma. In 2015 mid-April, the solar wind started to disappear from the observation region, to re-appear again in 2015 December. Low-energy cometary ions were seen at first when Rosetta was about 100 km from the nucleus at 3.6 au, and soon after consistently throughout the mission except during the excursions to farther distances from the comet. The observed flux of low-energy ions was relatively constant due to Rosetta's orbit changing with comet activity. Accelerated cometary ions, moving mainly in the antisunward direction gradually became more common as comet activity increased. These accelerated cometary ions kept being observed also after the solar wind disappeared from the location of Rosetta, with somewhat higher fluxes further away from the nucleus. Around perihelion, when Rosetta was relatively deep within the comet magnetosphere, the fluxes of accelerated cometary ions decreased, as did their maximum energy. The disappearance of more energetic cometary ions at close distance during high activity is suggested to be due to a flow pattern where these ions flow around the obstacle of the denser coma or due to charge exchange losses.

  • 15.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Box 812, 981 28 Kiruna, Sweden.
    Stenberg Wieser, Gabriella
    Swedish Institute of Space Physics, Box 812, 981 28 Kiruna, Sweden.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering. Swedish Institute of Space Physics, Box 812, 981 28 Kiruna, Sweden.
    Wedlund, Cyril Simon
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering, PO Box 13000, 00076 Aalto, Finland.
    Kallio, Esa
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering, PO Box 13000, 00076 Aalto, Finland.
    Gunell, Herbert
    Belgian Institute for Space Aeronomy, avenue Circulaire 3, 1180 Brussels, Belgium.
    Edberg, N. J. T.
    Swedish Institute of Space Physics, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, Sweden.
    Eriksson, Anders
    Swedish Institute of Space Physics, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, Sweden.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Box 812, 981 28 Kiruna, Sweden.
    Koenders, Christoph
    TU – Braunschweig, Institute for Geophysics and extraterrestrial Physics, Mendelssohnstr. 3, 38106 Braunschweig, Germany.
    Wieser, Martin
    Swedish Institute of Space Physics, Box 812, 981 28 Kiruna, Sweden.
    Lundin, Rickard
    Swedish Institute of Space Physics, Box 812, 981 28 Kiruna, Sweden.
    Barabash, Stas
    Swedish Institute of Space Physics, Box 812, 981 28 Kiruna, Sweden.
    Mandt, Kathleen E.
    Southwest Research Institute, 6220 Culebra Rd., San Antonio, TX 78238, USA.
    Burch, James L.
    Southwest Research Institute, 6220 Culebra Rd., San Antonio, TX 78238, USA.
    Goldstein, Raymond M.
    Southwest Research Institute, 6220 Culebra Rd., San Antonio, TX 78238, USA.
    Mokashi, Prachet
    Southwest Research Institute, 6220 Culebra Rd., San Antonio, TX 78238, USA.
    Carr, Chris
    Imperial College London, Exhibition Road, London SW7 2AZ, UK.
    Cupido, Emanuele
    Imperial College London, Exhibition Road, London SW7 2AZ, UK.
    Fox, P. T.
    Imperial College London, Exhibition Road, London SW7 2AZ, UK.
    Szego, Karoly
    Wigner Research Centre for Physics, 1121 Konkoly Thege street 29–33, Budapest, Hungary.
    Nemeth, Zoltan
    Wigner Research Centre for Physics, 1121 Konkoly Thege street 29–33, Budapest, Hungary.
    Fedorov, Andrei
    Institut de Recherche en Astrophysique et Planétologie, 31028 Toulouse, France.
    Sauvaud, J. A.
    Institut de Recherche en Astrophysique et Planétologie, 31028 Toulouse, France.
    Koskinen, Hannu
    University of Helsinki, Department of Physics, PO Box 64, University of Helsinki, 00014 Helsinki, Finland; Finnish Meteorological Institute, PO BOX 503, 00101 Helsinki, Finland.
    Richter, I.
    TU – Braunschweig, Institute for Geophysics and extraterrestrial Physics, Mendelssohnstr. 3, 38106 Braunschweig, Germany.
    Lebreton, J. -P.
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), UMR 7328 CNRS – Université d’Orléans, France.
    Henri, P.
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), UMR 7328 CNRS – Université d’Orléans, France.
    Volwerk, M.
    Space Research Institute, Austrian Academy of Sciences, Schmiedlstraße 6, 8042 Graz, Austria.
    Vallat, C.
    Rosetta Science Ground Segment, SRE-OOR, Office A006, European Space Astronomy Centre, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain.
    Geiger, B.
    Rosetta Science Ground Segment, SRE-OOR, Office A006, European Space Astronomy Centre, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain.
    Evolution of the ion environment of comet 67P/Churyumov-Gerasimenko2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 583, article id A20Article in journal (Refereed)
    Abstract [en]

    Context. The Rosetta spacecraft is escorting comet 67P/Churyumov-Gerasimenko from a heliocentric distance of >3.6 AU, where the comet activity was low, until perihelion at 1.24 AU. Initially, the solar wind permeates the thin comet atmosphere formed from sublimation. Aims. Using the Rosetta Plasma Consortium Ion Composition Analyzer (RPC-ICA), we study the gradual evolution of the comet ion environment, from the first detectable traces of water ions to the stage where cometary water ions accelerated to about 1 keV energy are abundant. We compare ion fluxes of solar wind and cometary origin. Methods. RPC-ICA is an ion mass spectrometer measuring ions of solar wind and cometary origins in the 10 eV-40 keV energy range. Results. We show how the flux of accelerated water ions with energies above 120 eV increases between 3.6 and 2.0 AU. The 24 h average increases by 4 orders of magnitude, mainly because high-flux periods become more common. The water ion energy spectra also become broader with time. This may indicate a larger and more uniform source region. At 2.0 AU the accelerated water ion flux is frequently of the same order as the solar wind proton flux. Water ions of 120 eV-few keV energy may thus constitute a significant part of the ions sputtering the nucleus surface. The ion density and mass in the comet vicinity is dominated by ions of cometary origin. The solar wind is deflected and the energy spectra broadened compared to an undisturbed solar wind.

  • 16.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden..
    Wieser, Gabriella Stenberg
    Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering. Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden.
    Wedlund, Cyril Simon
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering, Post Office Box 13000, FI-00076 Aalto, Finland.
    Gunell, Herbert
    Belgian Institute for Space Aeronomy, Avenue Circulaire 3, 1180 Brussels, Belgium.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden.
    Lundin, Rickard
    Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden.
    Barabash, Stas
    Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden.
    Wieser, Martin
    Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden.
    Carr, Chris
    Imperial College London, Exhibition Road, London SW7 2AZ, UK.
    Cupido, Emanuele
    Imperial College London, Exhibition Road, London SW7 2AZ, UK.
    Burch, James L.
    Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238, USA.
    Fedorov, Andrei
    Institut de Recherche en Astrophysique et Planétologie, Toulouse, France.
    Savaud, Jean-André
    Institut de Recherche en Astrophysique et Planétologie, Toulouse, France.
    Koskinen, Hannu
    Department of Physics, University of Helsinki, Post Office Box 64, FI-00014 Helsinki, Finland; Finnish Meteorological Institute, Post Office Box 503, FI-00101 Helsinki, Finland.
    Kallio, Esa
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering, Post Office Box 13000, FI-00076 Aalto, Finland; Finnish Meteorological Institute, Post Office Box 503, FI-00101 Helsinki, Finland.
    Lebreton, Jean-Pierre
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), UMR 7328 CNRS–Université d’Orléans, France.
    Eriksson, Anders
    Swedish Institute of Space Physics, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, Sweden.
    Edberg, Niklas
    Swedish Institute of Space Physics, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, Sweden.
    Goldstein, Raymond
    Belgian Institute for Space Aeronomy, Avenue Circulaire 3, 1180 Brussels, Belgium.
    Henri, Pierre
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), UMR 7328 CNRS–Université d’Orléans, France.
    Coenders, Christoph
    Technicsche Universität–Braunschweig, Institute for Geophysics and Extraterrestrial Physics, Mendelssohnstraße 3, D-38106 Braunschweig, Germany.
    Mokashi, Prachet
    Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238, USA.
    Nemeth, Zoltan
    Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest, Hungary.
    Richter, Ingo
    Technicsche Universität–Braunschweig, Institute for Geophysics and Extraterrestrial Physics, Mendelssohnstraße 3, D-38106 Braunschweig, Germany.
    Szego, Karoly
    Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest, Hungary.
    Volwerk, Martin
    Space Research Institute, Austrian Academy of Sciences, Schmiedlstraße 6, 8042 Graz, Austria.
    Vallat, Claire
    Rosetta Science Ground Segment, Science and Robotic Exploration (SRE-OOR), Office A006, European Space Astronomy Centre, Post Office Box 78, 28691 Villanueva de la Cañada, Madrid, Spain.
    Rubin, Martin
    Physikalisches Institut, University of Bern.
    Birth of a comet magnetosphere: A spring of water ions2015In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 347, no 6220, article id aaa0571Article in journal (Refereed)
    Abstract [en]

    The Rosetta mission shall accompany comet 67P/Churyumov-Gerasimenko from a heliocentric distance of >3.6 astronomical units through perihelion passage at 1.25 astronomical units, spanning low and maximum activity levels. Initially, the solar wind permeates the thin comet atmosphere formed from sublimation, until the size and plasma pressure of the ionized atmosphere define its boundaries: A magnetosphere is born. Using the Rosetta Plasma Consortium ion composition analyzer, we trace the evolution from the first detection of water ions to when the atmosphere begins repelling the solar wind (~3.3 astronomical units), and we report the spatial structure of this early interaction. The near-comet water population comprises accelerated ions (

  • 17.
    Saillenfest, Melaine
    et al.
    IMCCE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris 06, LAL, Université de Lille, Paris, 75014, France.
    Tabone, B
    LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris 06, Paris, 75014, France.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Solar wind dynamics around a comet: The paradigmatic inverse-square-law model2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 617, article id A99Article in journal (Refereed)
    Abstract [en]

    Aims.

    Observations of solar protons near comet 67P/Churyumov-Gerasimenko (67P) by the Rosetta spacecraft can be modelled by the planar motion in an effective magnetic field proportional to 1/r(2). We aim to provide a thorough study of such dynamics, with a clear description of the behaviour of an incoming flux of particles. We will be able, then, to calibrate the free parameters of the model to Rosetta observations. 

    Methods.

    Basic tools of dynamical analysis are used. They lead to a definition of the relevant parameters for the system and a classification of the possible types of trajectories. Using the so-obtained formalism, the structures formed by a flux of particles coming from infinity can be studied. 

    Results.

    All the trajectories are parametrised by two characteristic radii, r(E) and r(C), derived from first integrals. There are three different types of motion possible divided by a separatrix corresponding to r(E) = r(C). An analytical expression of the trajectories, defined by an integral, is developed. Using this formalism, the application to a flux of particles coming from infinity (modelling the incident solar wind) gives one free parameter only, the radius r(E), which scales the problem. A circular cavity of radius 0.28 r(E) is created, as well as an overdensity curve (analogous to a caustic in optics). At each observation time, r(E) can be calibrated to Rosetta plasma measurements, giving a qualitative understanding of the solar particle dynamics (incoming direction, cavity and density map). We also deduce that, in order to properly capture the essence of the dynamics, numerical simulations of the solar wind around a comet must use simulation boxes much larger than r(E) and grids much finer than r(E).

  • 18.
    Wedlund, Cyril Simon
    et al.
    Department of Physics, University of Oslo, Oslo, Norway.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Kallio, Esa
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Alho, Markku
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Gunell, Herbert
    Royal Belgian Institute for Space Aeronomy, Brussels, Belgium. Department of Physics, Umeå University, Umeå, Sweden.
    Bodewits, Dennis
    Physics Department, Auburn University, Auburn, AL, USA.
    Beth, Arnaud
    Department of Physics, Imperial College London, London, UK.
    Gronoff, Guillaume
    Science Directorate, Chemistry & Dynamics Branch, NASA Langley Research Center, Hampton, VA, USA. SSAI, Hampton, VA, USA.
    Hoekstra, Ronnie
    Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands.
    Solar wind charge exchange in cometary atmospheres: II. Analytical model2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A36Article in journal (Refereed)
    Abstract [en]

    Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet because they mass-load the solar wind through an effective conversion of fast, light solar wind ions into slow, heavy cometary ions. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provided a unique opportunity to study charge-changing processes in situ.

    Aims. To understand the role of charge-changing reactions in the evolution of the solar wind plasma and to interpret the complex in situ measurements made by Rosetta, numerical or analytical models are necessary.

    Methods. An extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines is presented. It is based on a thorough book-keeping of available charge-changing cross sections of hydrogen and helium particles in a water gas.

    Results. After presenting a general 1D solution of charge exchange at comets, we study the theoretical dependence of charge-state distributions of (He2+, He+, He0) and (H+, H0, H) on solar wind parameters at comet 67P. We show that double charge exchange for the He2+−H2O system plays an important role below a solar wind bulk speed of 200 km s−1, resulting in the production of He energetic neutral atoms, whereas stripping reactions can in general be neglected. Retrievals of outgassing rates and solar wind upstream fluxes from local Rosetta measurements deep in the coma are discussed. Solar wind ion temperature effects at 400 km s−1 solar wind speed are well contained during the Rosetta mission.

    Conclusions. As the comet approaches perihelion, the model predicts a sharp decrease of solar wind ion fluxes by almost one order of magnitude at the location of Rosetta, forming in effect a solar wind ion cavity. This study is the second part of a series of three on solar wind charge-exchange and ionization processes at comets, with a specific application to comet 67P and the Rosetta mission.

  • 19.
    Wedlund, Cyril Simon
    et al.
    Department of Physics, University of Oslo, Oslo, Norway.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Alho, Markku
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Kallio, Esa
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Gunell, Herbert
    Royal Belgian Institute for Space Aeronomy, Brussels, Belgium. Department of Physics, Umeå University, Umeå, Sweden.
    Bodewits, Dennis
    Physics Department, Auburn University, Auburn, USA.
    Heritier, Kevin
    Department of Physics, Imperial College London, London, UK.
    Galand, Marina
    Department of Physics, Imperial College London, London, UK.
    Beth, Arnaud
    Department of Physics, Imperial College London, London, UK.
    Rubin, Martin
    Space Research and Planetary Sciences, University of Bern, Bern, Switzerland.
    Altwegg, Kathrin
    Space Research and Planetary Sciences, University of Bern, Bern, Switzerland.
    Volwerk, Martin
    Space Research Institute, Austrian Academy of Sciences, Graz, Austria.
    Gronoff, Guillaume
    Science directorate, Chemistry & Dynamics branch, NASA Langley Research Center, Hampton, Virginia, USA. SSAI, Hampton, Virginia, USA.
    Hoekstra, Ronnie
    Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands.
    Solar wind charge exchange in cometary atmospheres: III. Results from the Rosetta mission to comet 67P/Churyumov-Gerasimenko2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A37Article in journal (Refereed)
    Abstract [en]

    Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provides a unique opportunity to study charge-changing processes in situ.

    Aims. To understand the role of these reactions in the evolution of the solar wind plasma and interpret the complex in situ measurements made by Rosetta, numerical or analytical models are necessary.

    Methods. We used an extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines. The model is driven by solar wind ion measurements from the Rosetta Plasma Consortium-Ion Composition Analyser (RPC-ICA) and neutral density observations from the Rosetta Spectrometer for Ion and Neutral Analysis-Comet Pressure Sensor (ROSINA-COPS), as well as by charge-changing cross sections of hydrogen and helium particles in a water gas.

    Results. A mission-wide overview of charge-changing efficiencies at comet 67P is presented. Electron capture cross sections dominate and favor the production of He and H energetic neutral atoms (ENAs), with fluxes expected to rival those of H+ and He2+ ions.

    Conclusions. Neutral outgassing rates are retrieved from local RPC-ICA flux measurements and match ROSINA estimates very well throughout the mission. From the model, we find that solar wind charge exchange is unable to fully explain the magnitude of the sharp drop in solar wind ion fluxes observed by Rosetta for heliocentric distances below 2.5 AU. This is likely because the model does not take the relative ion dynamics into account and to a lesser extent because it ignores the formation of bow-shock-like structures upstream of the nucleus. This work also shows that the ionization by solar extreme-ultraviolet radiation and energetic electrons dominates the source of cometary ions, although solar wind contributions may be significant during isolated events.

  • 20.
    Wedlund, Cyril Simon
    et al.
    Department of Physics, University of Oslo, Oslo, Norway.
    Bodewits, Dennis
    Physics Department, Auburn University, Auburn, USA.
    Alho, Markku
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Hoekstra, Ronnie
    Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Gronoff, Guillaume
    Science directorate, Chemistry & Dynamics branch, NASA Langley Research Center, Hampton, Virginia, USA. SSAI, Hampton, Virginia, USA.
    Gunell, Herbert
    Royal Belgian Institute for Space Aeronomy, Brussels, Belgium. Department of Physics, Umeå University, Umeå, Sweden.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Kallio, Esa
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Beth, Arnaud
    Department of Physics, Imperial College London, London, UK.
    Solar wind charge exchange in cometary atmospheres: I. Charge-changing and ionization cross sections for He and H particles in H2O2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A35Article in journal (Refereed)
    Abstract [en]

    Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet, mass-loading the solar wind through an effective conversion of fast light solar wind ions into slow heavy cometary ions.

    Aims. To understand these processes and place them in the context of a solar wind plasma interacting with a neutral atmosphere, numerical or analytical models are necessary. Inputs of these models, such as collision cross sections and chemistry, are crucial.

    Methods. Book-keeping and fitting of experimentally measured charge-changing and ionization cross sections of hydrogen and helium particles in a water gas are discussed, with emphasis on the low-energy/low-velocity range that is characteristic of solar wind bulk speeds (<20 keV u−1/2000 km s−1).

    Results. We provide polynomial fits for cross sections of charge-changing and ionization reactions, and list the experimental needs for future studies. To take into account the energy distribution of the solar wind, we calculated Maxwellian-averaged cross sections and fitted them with bivariate polynomials for solar wind temperatures ranging from 105 to 106 K (12–130 eV).

    Conclusions. Single- and double-electron captures by He2+ dominate at typical solar wind speeds. Correspondingly, single-electron capture by H+ and single-electron loss by H dominate at these speeds, resulting in the production of energetic neutral atoms (ENAs). Ionization cross sections all peak at energies above 20 keV and are expected to play a moderate role in the total ion production. However, the effect of solar wind Maxwellian temperatures is found to be maximum for cross sections peaking at higher energies, suggesting that local heating at shock structures in cometary and planetary environments may favor processes previously thought to be negligible. This study is the first part in a series of three on charge exchange and ionization processes at comets, with a specific application to comet 67P/Churyumov-Gerasimenko and the Rosetta mission.

  • 21.
    Wedlund, Cyril Simon
    et al.
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Kallio, Esa
    Finnish Meteorological Institute, Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Alho, Markku
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Wieser, Gabriella Stenberg
    Swedish Institute of Space Physics.
    Gunell, Herbert
    Swedish Institute of Space Physics / Institutet för rymdfysik , Belgian Institute for Space Aeronomy, Brussels.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Pusa, J.
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Gronoff, Guillaume
    Science Directorate, Chemistry and Dynamics Branch, NASA Langley Research Center, Hampton, Virginia.
    The atmosphere of comet 67P/Churyumov-Gerasimenko diagnosed by charge-exchanged solar wind alpha particles2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, article id A154Article in journal (Refereed)
    Abstract [en]

    Context. The ESA/Rosetta mission has been orbiting comet 67P/Churyumov-Gerasimenko since August 2014, measuring its dayside plasma environment. The ion spectrometer onboard Rosetta has detected two ion populations, one energetic with a solar wind origin (H+, He2+, He+), the other at lower energies with a cometary origin (water group ions such as H2O+). He+ ions arise mainly from charge-exchange between solar wind alpha particles and cometary neutrals such as H2O. Aims. The He+ and He2+ ion fluxes measured by the Rosetta Plasma Consortium Ion Composition Analyser (RPC-ICA) give insight into the composition of the dayside neutral coma, into the importance of charge-exchange processes between the solar wind and cometary neutrals, and into the way these evolve when the comet draws closer to the Sun. Methods. We combine observations by the ion spectrometer RPC-ICA onboard Rosetta with calculations from an analytical model based on a collisionless neutral Haser atmosphere and nearly undisturbed solar wind conditions. Results. Equivalent neutral outgassing rates Q can be derived using the observed RPC-ICA He+/He2+ particle flux ratios as input into the analytical model in inverse mode. A revised dependence of Q on heliocentric distance Rh in AU is found to be Rh -7.06Rh-7.06 between 1.8 and 3.3 AU, suggesting that the activity in 2015 differed from that of the 2008 perihelion passage. Conversely, using an outgassing rate determined from optical remote sensing measurements from Earth, the forward analytical model results are in relatively good agreement with the measured RPC-ICA flux ratios. Modelled ratios in a 2D spherically-symmetric plane are also presented, showing that charge exchange is most efficient with solar wind protons. Detailed cometocentric profiles of these ratios are also presented. Conclusions. In conclusion, we show that, with the help of a simple analytical model of charge-exchange processes, a mass-capable ion spectrometer such as RPC-ICA can be used as a "remote-sensing" instrument for the neutral cometary atmosphere.

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